1. Field of the Invention
The invention is concerned with a brazable shape memory alloy, .beta.-type brass alloy, and a method of brazing.
2. Description of the Prior Art
Shape memory alloys of the .beta.-brass type (Cu/Zn/Al system) are known (e.g. DE-05 2 711 576; DE-05 2 055 755; AT-PS 333 522). In general, alloys of this type are annealed between 600.degree. C. and 960.degree. C. depending on their composition in order to obtain the highest possible fraction of the .beta.-phase. They are thereupon quenched to below a critical temperature M.sub.s in order to obtain a metastable martensitic phase. M.sub.s can be above or below room temperature depending on the composition. On reheating in the course of subsequent processing (e.g., brazing or soldering) the metastable phase is extensively converted into the stable and the memory effect is lost.
It follows from the above that memory alloys of the type Cu/Zn/Al are, in general, not brazable without their principal physical property, the memory effect, being unacceptably impaired. The melting points of most technical soft solders are sufficiently high into the temperature range at which precipitation of stable phases occur that they can be eliminated from the outset as a method of joining components. On the other hand, brazing alloys have melting points which are in the range of annealing temperatures of the memory alloy and problems can arise from an overlap of these temperatures. Moreover .beta.-brass alloys have a tendency towards excessive grain growth at the high temperatures of brazing, leading to cracking susceptibility, so that joins made in this manner are rejected as being unusable.
A need therefore exists for a brazable shape memory alloy together with an associated brazing process, whereby the memory effect in the final assembled component can be fully used, without the need for additional processing steps or equipment, and wherein the grain growth of the memory alloy resulting from any heating is avoided and its cracking susceptibility effectively reduced.